The goal of this proposal is to design and build compact pixellated CdZnTe imaging arrays with high energy and spatial resolution for nuclear medical imaging. Specific applications that will benefit from the unique combination of high intrinsic spatial resolution, compact detector size, and high energy resolution offered by these solid state imagers will be multiple pinhole imagers and electronically collimated SPECT. We propose a new P-I-N detector design, which offers a significant advantage over current M-S-M detector arrays through reduced leakage current which can provide for lower noise and higher operating biases. The proposed P-I-N detector fabrication process is low-cost and amenable to production scale-up. In addition, the P-I-N design will allow the use of low-cost, low-resistivity, large-area vertical Bridgman-grown CdZnTe since it offers lower leakage current than a M-S-M design. In Phase I, Spire will develop 4 x 4 CdZnTe P-I-N photodiode arrays with pixel sizes in the range 1 mm x 1 mm to 0.5 mm x 0.5 mm. P and n layers will be deposited on an I-CdZnTe substrate to form a P-I-N device structure, and pixelated arrays will be fabricated by photolithography. Science Applications International Corporation (SAIC) will hybridize these photodiode arrays with Si circuitry and test for pixel-to-pixel uniformity. During Phase II, we will develop a new generation gamma camera using large CdZnTe photodiode arrays for medical imaging. Commercialization of this technology will be vigorously pursued. PROPOSED COMMERCIAL APPLICATION CdZnTe detector arrays with high energy resolution and sensitivity will be useful for breast imaging and brain imaging in nuclear medicine. In addition, these detectors can be used in X-ray astronomy, airport baggage scanners, nuclear verification system, non-destructive industrial imaging, and environmental monitoring.